The present invention relates to a cleaning agent which comprises an oxidizing agent and a chelating agent and to a process for producing semiconductor devices and substrates for liquid crystal display panels using said cleaning agent.
More particularly, the present invention relates to a cleaning process which comprises removing a layer of a photoresist and residues formed from a photoresist in the process for producing semiconductor integrated circuits, a process for cleaning glass substrates for liquid crystal display panels in the process for producing substrates for liquid crystal display panels and a cleaning process which comprises removing residues formed by dry etching in the production of thin film circuit devices made of materials such as tantalum, aluminum, chromium, niobium and indiumtin oxide (referred to as ITO, hereinafter) which are used for producing substrates for liquid crystal display panels.
Lithography has generally been used in the production of semiconductor devices such as IC and LSI and substrates for liquid crystal display panels. When semiconductor devices and substrates for liquid crystal display panels are produced in accordance with the lithography, in general, the following series of procedures are conducted: an insulation film such as a film of silicon oxide and a conductive thin film for conductive wirings such as a metal film are formed on a silicon wafer or a substrate made of a material such as glass; the thus formed films are uniformly coated with a photoresist and a photosensitive layer is formed on the films; the photosensitive layer is treated by selective exposure to light and development and a desired pattern of the photoresist is formed; using the formed pattern of the photoresist as a mask, the films of the lower layers are selectively etched and a pattern is formed; and then the pattern of the photoresist is completely removed. In recent years, semiconductors and substrates for liquid crystal display panels are integrated to greater degrees and formation of patterns having dimensions of a quarter micron or smaller are required. As the dimension of working becomes extremely small, dry etching is mainly used for the selective etching and ashing with oxygen plasma is used for the removal of the pattern of the photoresist.
However, in the dry etching, it is known that residues derived from the dry etching gas, the photoresist and the conductive thin film (referred to as resist residues, hereinafter) are formed in portions around the formed pattern. When the resist residues are present in portions around the pattern, in particular, inside and around via holes, undesirable phenomena such as an increase in resistance and short circuits arise. Therefore, to obtain semiconductor devices and substrates for liquid crystal display panels having high qualities, removal of the resist residues is very important.
Moreover, as the surface area of glass substrates for liquid crystals which are used for liquid crystal panels becomes greater, display devices tend to have a greater number of pixels. Under such circumstances, the degree of cleaning of the entire surface of glass substrates for liquid crystals is directly related to the yield of the production and, as the result, improvement in the cleaning ability is strongly desired.
As the cleaning agent for glass substrates for liquid crystals, alkali cleaning agents such as inorganic alkalis and organic alkalis and acid cleaning agents such as sulfuric acid, hydrofluoric acid and buffered hydrofluoric acid are currently used. However, the cleaning agents using inorganic alkalis have a problem in that alkali ions are adsorbed to the substrates and remain there after the cleaning and the residual alkali ions occasionally cause problems on electric properties of the substrates, in particular, the substrates of thin film transistors (TFT). The cleaning agents using organic alkalis have a problem in that a sufficient effect of cleaning cannot be obtained and adhesion of thin films formed in the succeeding steps occasionally becomes poor. Moreover, when the cleaning is conducted using a conventional cleaning agent, minute roughness of the surface of glass substrates as damages formed by the etching and minute particles also formed by the etching are not completely removed. These problems are becoming crucial as the liquid crystals are more highly integrated and the surface area of the glass substrates increases. It is strongly desired that an effective method to overcome these problems is developed.
As the process for removing resist residues, cleaning liquids of organic amine which comprise mixtures of alkanolamines and organic solvents are disclosed in Japanese Patent Application Laid-Open Nos. Showa 62(1987)-49355 and Showa 64(1989)-42653. These cleaning liquids have drawbacks in that the cleaning liquids are flammable because relatively high temperatures are required for the treatment and flammable organic compounds in the cleaning liquids are vaporized and that metal films are corroded because the organic amines are alkaline when rinsing is conducted with water alone without an organic solvent such as an alcohol after the removal of resist residues and, therefore, rinsing with an organic solvent such as an alcohol is necessary. Aqueous solutions of fluorine comprising fluorine compounds, organic solvents and corrosion inhibitors which exhibit greater ability to remove resist residues than the cleaning liquids of organic amines do and can be used at lower temperatures are disclosed in Japanese Patent Application Laid-Open Nos. Heisei 7(1995)-201794 and Heisei 8(1996)-20205.
In recent years, the conditions are becoming harder in treatments such as dry etching and ashing in the process for producing semiconductor devices and substrates for liquid crystal display panels. Photoresists have greater transformation due to this change in the conditions and complete removal of resist residues cannot be achieved by using the above cleaning liquids of alkalis or the above aqueous solutions of fluorine. When the resist residues are not removed completely and left remaining, electrical troubles such as an increase in resistance, breaking of wirings, short circuits and disorder in wirings arise. Therefore, a cleaning agent which can achieve complete removal of resist residues is strongly desired.
Moreover, when the cleaning liquids of organic amines are used, residues containing tantalum left after dry etching are hardly removed. To remove the residues containing tantalum completely, a cleaning agent containing fluorine such as buffered hydrofluoric acid is used after the dry etching. However, the cleaning agent containing fluorine has a problem in that materials of switching devices such as amorphous silicon and polysilicon and glass substrates are corroded.
An object of the present invention is to provide a cleaning agent which can effectively remove resist residues formed in the process for producing semiconductor devices and residues derived from conductive thin films of metals formed, photoresist films used as the etching mask and contaminants on glass substrates in the process for producing substrates for liquid crystal display panels.
Another object of the present invention is to provide a cleaning process in which a photoresist forming a mask on inorganic or plastic substrates and resist residues remaining after dry etching can be removed in a short time in the wiring process of semiconductors used in semiconductor integrated circuits while no wiring materials or insulating materials are corroded.
Still another object of the present invention is to provide a process for cleaning glass substrates for liquid crystals which are used in the process for producing liquid crystal display panels.
Still another object of the present invention is to provide a cleaning process in which residues formed by dry etching for formation of thin circuits on glass substrates are removed easily while the glass substrates, the thin film circuit devices or the wiring materials are not corroded at all and substrates for liquid crystal display panels can be cleaned very efficiently.
As the result of intensive studies by the present inventors to achieve the above objects, a cleaning agent which comprises an oxidizing agent and a chelating agent and a process for cleaning using this cleaning agent were discovered. The present invention has been completed based on the knowledge.
As the first embodiment of the present invention, a cleaning agent comprises 0.1 to 60% by weight of an oxidizing agent and 0.0001 to 5% by weight of a chelating agent.
As the second embodiment of the present invention, a process for cleaning semiconductor devices comprises coating an inorganic or plastic substrate with a photoresist film, forming a mask with the photoresist film, dry etching portions of the substrate which are not covered with the mask and removing residues of the photoresist formed by the dry etching and/or the photoresist film forming the mask with a cleaning agent described above. In the above process, where desired, ashing may be conducted after the dry etching and resist residues formed by the dry etching may be removed with the above cleaning agent thereafter.
As the third embodiment of the present invention, a process for cleaning substrates for liquid crystal display panels comprises forming a conductive thin film on a glass substrate; forming a prescribed pattern with a photoresist on the conductive thin film; using the pattern of the photoresist as an etching mask, removing portions of the conductive film which are not covered with the pattern of the photoresist by dry etching; and removing residues derived from the conductive thin film which are formed by the dry etching with a cleaning agent described above. In the above process, where desired, ashing may be conducted after the dry etching and residues may be removed with the above cleaning agent thereafter.